This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-275517, filed Sep. 29, 1999; and No. 2000-218299, filed Jul. 19, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a polishing method for polishing a worked object, and more particularly to a dresser for use in dressing a polishing work surface of a polishing apparatus.
Production of articles may require a step of polishing materials constituting the articles in large quantities with high accuracy by means of a polishing work surface, for example, a surface of a polishing cloth. The materials to be polished may be plate objects, such as silicon wafers, ceramic boards and SOI (Silicon On Insulator) boards, or objects other than the plate objects, such as magnetic heads for use in magnetic recording apparatuses or prisms for use in optical apparatuses.
In the aforementioned step, the conditions of the surface of the polishing cloth vary from batch to batch due to being clogged with chippings from the polished objects. Therefore, the polished amount or the flatness of the polished object in the same working time may vary unless some measure is taken. Therefore, it is necessary to perform a process for dressing the polishing work surface made of the surface of the polishing cloth in order to keep the work surface in the same, uniform condition in every batch.
FIGS. 5A and 5B show a dresser having a dressing member. The dressing member 21 of the dresser, mounted on a base board 20, is cylindrical, having an outer diameter of about 28 cm, an inner diameter of about 26 cm, and a thickness of about 2 cm. The dresser is screwed to a jig 23 via screw holes formed in the base board 20. The dressing member 21 has recesses 22 arranged at almost regular intervals to allow passage of a polishing liquid. Conventionally, the dresser having the above structure is brought into contact with a rotating polishing cloth, while it is rotating about a center O of the base board 20, thereby performing a dressing process.
In the dressing process, the surface of the polishing cloth must be abraded by about 1 xcexcm each time polishing is performed, from the viewpoint of insuring precision of the shape of the articles and stability of the work condition. When the polishing cloth is abraded about 1 mm from the initial state, it is at the end of its life and exchanged for a new one.
According to the conventional art, even when a portion of the polishing cloth, which directly contributes to polishing of wafers, is still usable, an outer or inner periphery of the polishing work surface is excessively thinned. If an outer or inner periphery of the polishing work surface is worn by a given amount or more, while a portion of the polishing cloth which directly contributes to polishing of wafers is still available for polishing, the balance of the tension and the like exerted on the polishing cloth will be lost and the polishing condition will be unstable. In this case, it will be difficult to polish the object with high accuracy. Therefore, the polishing cloth must be exchanged.
A first object of the present invention is to provide a dresser which suppresses variation in the amount of work in dressing, and a polishing apparatus using the dresser.
To achieve this object, there is provided a dresser approachable to and separable from a polishing surface of a polishing apparatus, and having a dressing surface to be brought into contact with the polishing surface, the dressing surface being shaped as a substantially hollow triangle or a substantially hollow oval, or a dresser rotatable about a rotation axis and approachable to and separable from a polishing surface of a polishing apparatus by means of the rotation axis, wherein the dresser can be arranged on the polishing apparatus such that, in a region where the polishing surface actually polishes an object, an integral of a function of a product of a time during which the polishing surface is in contact with the dressing member and a relative velocity at a time when the polishing surface contacts to the dressing member, with respect to a dressing time, is at least equal to that in inner and outer peripheral portions of the polishing surface.
A second object of the present invention is to provide a polishing method which suppresses variation in the amount of work in dressing.
To achieve this object, there is provided a method for producing an article, comprising: a dressing step for bringing any dresser mentioned above into contact with a polishing surface; and a polishing step for, after the dressing step, bringing an object into contact with the polishing surface, thereby polishing the object.
According to the present invention, the lifetime of the polishing work surface can be prolonged. Thus, since the number of times of exchanging the polishing cloth is substantially reduced, the lead time required for production of articles can be reduced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.